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Benthic macrofauna abundance and biomass in the muddy region in southeast of the island of Helgoland (North Sea)

Benthic macrofauna were sampled on expedition HE625 of the R/V Heincke in July 2023 at 50 stations spread evenly over the muddy sediment region in southeast of the island of Helgoland (southeastern North Sea). At each station, two replicate samples were taken with a van Veen grab with a sampling area of 0.1 m² and a penetration depth of 10 cm. The first sample was sieved through a 1000 µm mesh to retain macrofauna, and species were determined to the lowest taxonomic level. The WoRMS LSIDs (AphiaID) was provided to identify the scientific name of the species. For each taxon, the total wet weight was measured with a precision of 0.001 g. The dataset comprises counted abundance and biomass records for 171 infaunal taxa.

Temperature effects on a plankton community from Helgoland Roads tested in an indoor mesocosm experiment in March 2022

To investigate the effect of temperature on a North Sea spring bloom community, we performed an incubation experiment in the mesocosm facility of the Institute for Chemistry and Biology of the Marine Environment (ICBM) in Wilhelmshaven. The plankton community was sampled from the long-term ecological research station Helgoland Roads (https://deims.org/1e96ef9b-0915-4661-849f-b3a72f5aa9b1) on the 6ᵗʰ of March, 2022. Collection of the surface community was conducted from the RV Heincke with a pipe covered with a 200 µm net that was attached to a diaphragm pump. The month-long incubation was started on the 7ᵗʰ of March in twelve indoor mesocosms, the Planktotrons (Gall et al., 2017). We chose three temperatures along the ascending part of the thermal performance curve (TPC) of the in situ community: the minimum temperature for positive growth (6°C, also the field temperature), the middle between the minimum and the optimum temperature (12 °C), and the optimum temperature for growth (18 °C). Ramping up the temperatures was conducted by 1 °C per day until the treatment temperatures were reached, resulting in a ramp phase (first twelve days) and a constant temperature phase. This dataset comprises all data collected within the experiment. Temperature, oxygen, pH, salinity, and in vivo fluorescence were measured daily at 10 am. Samples for dissolved nutrients (nitrate, nitrite, phosphate, silicate), chlorophyll a, DNA, particulate nutrients (biogenic silica, particulate organic carbon/nitrogen/phosphorus), as well as flow cytometric counts of bacteria (stained) and the unstained community were sampled every third day at the same time. The mesocosm water was generally filtered over a 200 µm mesh before sampling to exclude mesozooplankton. However, due to the appearance of large Phaeocystis colonies, additional samples without pre-filtration were taken for particulate organic carbon, nitrogen, phosphorus, and chlorophyll a starting on incubation day 15. PAR, total nitrogen and phosphorus as well as total alkalinity were measured at the start, in the middle, and at the end of the incubation. Samples for Mesozooplankton enumeration were taken and plankton species identified at the end of the experiment. All analysis scripts can be found on github (https://github.com/AntoniaAhme/TopTrons22MesocosmIncubation). The sequence data are available at the European Nucleotide Archive (ENA).

Monitoring of sandy beach meiofauna before and after sand nourishment (Ahrenshoop, Baltic Sea): metabarcoding data (number of reads per operational taxonomic unit)

We provide metabarcoding data (number of reads per operational taxonomic unit, OTU) determined from sediment samples collected on the sandy-beach water line of Ahrenshoop (Baltic Sea). Five sampling stations lay within the zone impacted by the sand nourishment between the boundary of the nature reserve in the north east and a site just north of the breakwater (AH01-AH05). An unaffected reference station was located south of Ahrenshoop (close to Niehagen) at the end of the road Pappelallee (PAP). Samples were collected at four dates. The first sampling was carried out before the sand nourishment took place (T0: 14 and 16 September 2021). Three samplings were realised after the impact: T1 (23 March 2022), T2 (27 September 2022), and T3 (28 March 2023). Latitude and longitude of each sampling location per station were recorded at each sampling date using a hand-held GPS application on a mobile phone. At the stations sampling locations varied over time. Prior to the sand nourishment the beach was narrow due to sand erosion in previous years. After the nourishment the additional extent of the beach was approximately 40 m at sampling date T1. Subsequently, progressive sand erosion forced the sampling locations (situated at the water line) further inland at T2 and T3. Samples were taken from the beach-water interface (water line) in the middle of the area between two groynes. Plexiglass cores (inner core diameter 5.4 cm) were inserted vertically into the sediment down to 15 cm depth. Each core was sliced in 5 cm-layers (0-5, 5-10 and 10-15 cm). Sediment horizons were preserved in 96-99% ethanol. Three cores (2 cores at T0) per sampling date were taken for metabarcoding analyses. The organisms were extracted by decantation over a 32-μm sieve. Genomic DNA was extracted from the filters using the DNeasy PowerSoil pro kit (Qiagen). Realtime-PCR was performed to amplify V1&V2, two hypervariable regions of 18S rDNA gene. The sequencing run was performed using the MiSeq Reagent Nanokit v2 (250 cycles paired end) on an Illumina MiSeq platform at the DZMB Metabarcoding lab in Wilhelmshaven, Germany. High-resolution amplicon sequence variants (ASVs) were obtained and compared to the NCBI database to assign taxonomic information to each ASV. The target meiofauna ASVs were further classified into operational taxonomic units (OTUs) with a 3% cut-off threshold using the statistical software R. Here, we present two Tables: (1) the taxonomic description of the 843 OTUs and their assigned ID number; (2) the number of reads per OTU per sample. The metabarcoding data are part of a larger ecological study on the influence of sand nourishment on meiofauna communities, which included grain-size and meiofauna abundances (see Related to and Supplement to).

Monitoring of sandy beach meiofauna before and after sand nourishment (Ahrenshoop, Baltic Sea): abundance data of meiofauna higher taxa

We provide abundance data for meiofauna taxa determined from sediment samples collected on the sandy-beach water line of Ahrenshoop (Baltic Sea). Five sampling stations lay within the zone impacted by the sand nourishment between the boundary of the nature reserve in the north east and a site just north of the breakwater (AH01-AH05). An unaffected reference station was located south of Ahrenshoop (close to Niehagen) at the end of the road Pappelallee (PAP). Samples were collected at four dates. The first sampling was carried out before the sand nourishment took place (T0: 14 September 2021). Three samplings were realised after the impact: T1 (23 March 2022), T2 (27 September 2022), and T3 (28 March 2023). Latitude and longitude of each sampling location per station were recorded at each sampling date using a hand-held GPS application on a mobile phone. At the stations sampling locations varied over time. Prior to the sand nourishment the beach was narrow due to sand erosion in previous years. After the nourishment the additional extent of the beach was approximately 40 m at sampling date T1. Subsequently, progressive sand erosion forced the sampling locations (situated at the water line) further inland at T2 and T3. Samples were taken from the beach-water interface (water line) in the middle of the area between two groynes. Plexiglass cores (inner core diameter 5.4 cm) were inserted vertically into the sediment down to 15 cm depth. Each core was sliced in 5 cm-layers (0-5, 5-10 and 10-15 cm). Sediment horizons were preserved in 96-99% ethanol. The organisms were extracted by decantation over a 32-μm sieve. The total number of individuals per taxon was counted and is presented as individuals per 10 cm². In the framework of our monitoring samples were primarily taken for a large-scale metabarcoding study on meiofauna communities. One core per station and sampling date was reserved for morphology-based community analyses. Here we present the results for the stations AH01, AH03, AH05, and PAP. We selected these stations because of their location at both ends and in the center of the impacted zone (AH01, AH03, AH05) and at the control site (PAP). The meiofauna (32-1000 µm) was mostly represented by Copepoda, Nematoda, Platyhelminthes, Gastrotricha, and some Annelida. We counted 27445 individuals in total, encompassing 10 higher taxa. We counted copepod nauplii separately due to their small body size. We defined the combined group "Plathyhelminthes+Diurodrilus sp." because members of the annelid genus Diurodrilus sp. are not distinguishable from Platyhelminthes under the stereomicroscope. The meiofauna abundance data are part of a larger ecological study on the influence of sand nourishment on meiofauna communities, which included grain-size and metabarcoding analyses (see Related to and Supplement to).

Thermal performance assay of a plankton community from Helgoland Roads for an indoor mesocosm experiment  in March 2022

To choose the treatment temperatures for an indoor mesocosm temperature experiment at the ICBM in Wilhelmshaven (https://doi.pangaea.de/10.1594/PANGAEA.961155), a thermal performance curve assay was performed from the 8th of March until the 16th of March. It was started one day after filling the mesocosms with seawater from Helgoland Roads (https://deims.org/1e96ef9b-0915-4661-849f-b3a72f5aa9b1) by randomly spreading pooled sample water in 50 ml culture flasks across ten temperatures (3 °C to 30 °C in 3 °C steps) in triplicates. Their fluorescence (395/680 Excitation/Emission) was measured daily using a SYNERGY H1 microplate reader (BioTek, Winooski, Vermont, USA).

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